The present invention relates to a refrigerating apparatus and more particularly to a refrigerating apparatus for stores suited for refrigerating a plurality of showcases connected together with large load variations.
In conventional refrigerating apparatuses described, for example, in JP-A-8-271063, it has been known that a capacity-up pressure value and a capacity-down pressure value are determined for set pressures, and when a suction pressure has at least the capacity-up pressure value, the number of compressors being operated or the operating frequency is increased to raise the operating capacity, and when the suction pressure has at most the capacity-down pressure value, the number of compressors being operated or the operating frequency is reduced, and that the set pressure values are automatically changed according to temperatures detected inside and outside a store.
In the prior technique described above, when a load is large and frequently fluctuates, and a set pressure range is decreased in order to provide for fine operation at an optimum operating pressure, it is inevitable to repeat on/off operation of a compressor or to frequently change the inverter frequency. Therefore, there has been a fear that power consumption involved in on/off operation is made large in loss at the startup and with an inverter compressor, power consumption involved in a change in revolution is made large in loss.
An object of the present invention is to provide a highly reliable refrigerating apparatus, which is made optimum in operating pressure for a load of large fluctuations and is effective in energy saving.
To achieve the above objective, the present invention provides a refrigerating apparatus comprising a refrigerating cycle having compressors, a condenser, a liquid receiver, expansion valves and evaporators; and a suction pressure sensor for detecting a pressure on suction sides of the compressors; wherein when the suction pressure has at least a capacity-up pressure value, it causes an increase in the number of compressors being operated or the operating frequency; and when the suction pressure has at most a capacity-down pressure value, it causes reduction in the number of compressors being operated or the operating frequency; wherein when a time period, in which the suction pressure remains in at least the capacity-up pressure value, and a time period, in which the suction pressure remains in at most the capacity-down pressure value, are compared with each other and calculated, and the latter time period is longer than the former time period, at least one of the capacity-up pressure value and the capacity-down pressure value is made larger than said each pressure value (the capacity-up pressure value or the capacity-down pressure value).
Thereby, a time period of operation at the minimum required operating capacity is extended, which is effective in energy saving to enable reducing an amount of electric power consumed, and the number of on/off times of the compressor or a change in operating frequency is reduced, which can reduce power loss for a refrigerating capacity provided by a refrigerating machine.
In the above-mentioned refrigerating apparatus, when the time period, in which the suction pressure remains in at most the capacity-down pressure value, is shorter than the time period, in which the suction pressure remains in at least the capacity-up pressure value, at least one of the capacity-up pressure value and the capacity-down pressure value is made smaller than said each pressure value.
Further, the present invention provides a refrigerating apparatus comprising a refrigerating cycle having compressors, a condenser, a liquid receiver, expansion valves and evaporators; and a suction pressure sensor for detecting a pressure on suction sides of the compressors; wherein when the suction pressure has at least a capacity-up pressure value, it causes an increase in the number of compressors being operated or the operating frequency; and when the suction pressure has at most a capacity-down pressure value, it causes reduction in the number of compressors being operated or the operating frequency; and wherein when a rate of a change in the suction pressure is larger than a predetermined value, at least one of the capacity-up pressure value and the capacity-down pressure value is made larger than said each pressure value.
Further, in the above-mentioned refrigerating apparatus, when the rate of a change in the suction pressure is smaller than the predetermined value, at least one of the capacity-up pressure value and the capacity-down pressure value is made smaller than said each pressure value.
Further, according to the present invention, the compressors are plural in number, and when a time period having lapsed from a point of time, at which the suction pressure has at least the capacity-up pressure value, to a point of time, at which one of the plurality of the compressors stops, is determined, and is shorter than a predetermined time period, at least one of the capacity-up pressure value and the capacity-down pressure value is made larger than said each pressure value.
Further, in the above-mentioned refrigerating apparatus, when the time period having elapsed until the stoppage of one of the plurality of the compressors is longer than the predetermined duration, at least one of the capacity-up pressure value and the capacity-down pressure value is desirably made smaller than said each pressure value.
Further, according to the present invention, a time period having lapsed from a point of time, at which the suction pressure has at least the capacity-up pressure value, to a point of time, at which the suction pressure has at most the capacity-up pressure value, is determined, and is shorter than a predetermined duration, at least one of the capacity-up pressure value and the capacity-down pressure value is made larger than said each pressure value.
Further, in the above-mentioned refrigerating apparatus, when a rate of a change in the suction pressure is larger than a predetermined value, at least one of the capacity-up pressure value and the capacity-down pressure value is made larger than said each pressure value.